The ultimate goal of this project is to gain a scientific understanding of the origins and the mechanisms of human tactile sense: how shape, softness and surface texture of objects indented, stroked or vibrated on the primate fingertip skin are encoded by populations of mechanoreceptors. For these stimuli, a quantitative understanding of what spatio-temporal loads are imposed on the skin, how they are transmitted through the skin, and which mechanical signals are transduced by each type of spatially distributed mechanoreceptor populations is sought. Whereas the focus in the previous grant periods has been on the mechanical behavior of the fingertip as a whole, in this proposal the focus is on the mechanics of individual fingerpad ridges and grooves and its impact on Meissner corpuscle and Merkel disc locations. Building on the understanding gained with the use of robotic stimulators, imaging systems, and computational models developed over the previous grant period, new technologies and experimental methods will be brought to bear upon the problem. All the experiments listed below will be conducted on human and monkey fingerpads in vivo. The specific aims of this proposal are (1) to obtain high resolution anatomical and strain images of the fingerpad skin ridges and grooves using Optical Coherance Tomography, Ultrasound Backscatter Microscopy, and Video microscopy, (2) to measure the spatial distribution of pressure at the object-finger ridge contact interface using custom developed micro-electromechanical sensor arrays, (3) to obtain fingerpad skin and ridge impedance data using a high precision tactile stimulator, (4) to use the data from experiments to further improve high resolution 3D computational models of the fingerpad and perform finite element simulations involving contact with shaped and soft objects, and (5) to use the results from proposed biomechanical and previous neurophysiological experiments together with realistic computer models to develop a deeper understanding of the role of skin biomechanics in mechanoreceptor response. The benefits of this research include the delineation of the role of tissue mechanics from receptor dynamics in peripheral neural response, as well as eventually aiding the differentiation of the roles of peripheral and central mechanisms in somatosensory information processing. One example of a long-term benefit from a clinical standpoint will be the ability to design better tests for the evaluation of tactile sensibility of normal and impaired hands to aid diagnosis, treatment and rehabilitation. Another example of a spin-off application is that the Ultrasound Backscatter Microscope developed in the previous grant period has shown promise in imaging skin lesions in vivo.